“The ex-governor also pointed out that all the oxygen tanks which were previously placed at intervals along the rescue route in the cave from the forward command at Chamber 3 to the mound where the rest of the survivors are now sheltering have been used up and replacement oxygen tanks will be placed again.” http://englishnews.thaipbs.or.th/next-operation-bring-rest-safety-begin-10-20-hours-ex-governor-narongsak/
It was mentioned that there may be a hundred rescuers in the cave. The entire operation uses an enormous amount of O2.